package sbt

/** Define our settings system */

// A basic scope indexed by an integer.
final case class Scope(index: Int)

// Extend the Init trait.
//  (It is done this way because the Scope type parameter is used everywhere in Init.
//  Lots of type constructors would become binary, which as you may know requires lots of type lambdas
//  when you want a type function with only one parameter.
//  That would be a general pain.)
object SettingsExample extends Init[Scope]
{
	// Provides a way of showing a Scope+AttributeKey[_]
	val showFullKey: Show[ScopedKey[_]] = new Show[ScopedKey[_]] {
		def apply(key: ScopedKey[_]) = key.scope.index + "/" + key.key.label
	}

	// A sample delegation function that delegates to a Scope with a lower index.
	val delegates: Scope => Seq[Scope] = { case s @ Scope(index) =>
		s +: (if(index <= 0) Nil else delegates(Scope(index-1)) )
	}

	// Not using this feature in this example.
	val scopeLocal: ScopeLocal = _ => Nil

	// These three functions + a scope (here, Scope) are sufficient for defining our settings system.
}

/** Usage Example **/

object SettingsUsage
{
	import SettingsExample._
	import Types._

		// Define some keys
	val a = AttributeKey[Int]("a")
	val b = AttributeKey[Int]("b")

		// Scope these keys
	val a3 = ScopedKey(Scope(3), a)
	val a4 = ScopedKey(Scope(4), a)
	val a5 = ScopedKey(Scope(5), a)

	val b4 = ScopedKey(Scope(4), b)

		// Define some settings
	val mySettings: Seq[Setting[_]] = Seq(
		setting( a3, value( 3 ) ),
		setting( b4, app(a4 :^: KNil) { case av :+: HNil => av * 3 } ),
		update(a5)(_ + 1)
	)

		// "compiles" and applies the settings.
		//  This can be split into multiple steps to access intermediate results if desired.
		//  The 'inspect' command operates on the output of 'compile', for example.
	val applied: Settings[Scope] = make(mySettings)(delegates, scopeLocal, showFullKey)

		// Show results.
/*	for(i <- 0 to 5; k <- Seq(a, b)) {
		println( k.label + i + " = " + applied.get( Scope(i), k) )
	}*/

/** Output:
* For the None results, we never defined the value and there was no value to delegate to.
* For a3, we explicitly defined it to be 3.
* a4 wasn't defined, so it delegates to a3 according to our delegates function.
* b4 gets the value for a4 (which delegates to a3, so it is 3) and multiplies by 3
* a5 is defined as the previous value of a5 + 1 and
*   since no previous value of a5 was defined, it delegates to a4, resulting in 3+1=4.
* b5 isn't defined explicitly, so it delegates to b4 and is therefore equal to 9 as well
a0 = None
b0 = None
a1 = None
b1 = None
a2 = None
b2 = None
a3 = Some(3)
b3 = None
a4 = Some(3)
b4 = Some(9)
a5 = Some(4)
b5 = Some(9)
**/
}
